Although you’ve seen it on TV, there is no comparison to being part of a “wave” at a sporting event. Not only does the wave look really impressive as it makes its way around the stadium towards you, but you also end up feeling like you’ve contributed in a small way to a greater whole. And who knows, you may even find yourself on some highlight videos during the next local news broadcast.
Like the wave in a stadium, printed circuit board wave soldering is designed to touch as many participants as possible. However, in this case, the participants are the components on your PCB instead of the spectators in an arena. Wave soldering is the oldest form of soldering used in the mass production of circuit boards, and it is still used today to a great extent. Let’s look at the process of wave soldering and learn more about how component orientation can make a big difference in the manufacturability of your circuit board.
| Soldering Processes Used in Printed Circuit Board Manufacturing | |
|---|---|
| Wave Soldering | Used for thru-hole components and some discrete SMT parts |
| Solder Reflow | Best for SMT components, including fine-pitch devices |
| Selective Soldering | Used for heat-sensitive thru-hole components, tight part placements, concerns about collateral thermal damage, or quick-builds and prototypes |
| Hand Soldering | Best for low-volume builds and thru-hole components with odd shapes and pin configurations, as well as touch-ups of automated soldering processes |
Everything You’ve Always Wanted to Know About Wave Soldering but Have Never Asked
Following the war in the late 1940s, electronic devices quickly increased in popularity, and it soon became apparent that individually soldering each lead and wire was not practical for mass production. Initially, appliance manufacturers soldered circuit boards by dipping them into liquid flux followed by molten solder, but this was slow and problematic. Production teams needed a new method of automatically applying fresh solder alloy, and the precursor to the modern wave soldering system was introduced in the mid-1950s. This new system pumped molten solder through a nozzle to create a wave for the joints needing to be soldered to pass through.
Although wave soldering has been used for a long time, it is still essential to the circuit board assembly process. Thru-hole parts are typically wave-soldered, and some surface mount parts can be too. The circuit board is moved through the wave machine on a conveyor belt, passing over the molten solder. The wave action forces the molten solder up through the board’s holes and around their inserted pins to create a solid solder joint. Wave soldering is still highly favored because it can solder many boards quickly with less setup time than other methods.
To prepare for wave soldering, the manufacturer will check the printed circuit board for fit and set up with spacers for heat dissipation and the height of components on the board. These spacers will later dissolve in the wash tanks. The board will also have areas masked off where solder is not desired and may also be fitted with a fixture to protect bottom-side components if necessary. At the same time, technicians will heat the solder chemistry to 500 degrees Fahrenheit and adjust the wave solder’s conveyor system for speed and wave height to match the board’s parameters. These adjustments to the conveyor belt’s speed and height give the manufacturer precise control over soldering times and temperatures.
At this point, the boards are ready to be soldered, but the soldering process’s success will ultimately depend on how the parts are arranged on the board.
The Importance of Component Orientation for Wave Soldering
The success rate of wave soldering circuit boards depends on how well the part placement is optimized. The location and orientation of the parts can make a huge difference in how well the board is soldered. Here are some crucial points to keep in mind during component placement:
- Surface mount components placed on the back side of the board will be a problem if they are too close to thru-hole pins. The location of the SMT parts may make it difficult to fashion the fixture correctly, which could block the thru-hole pins from the full force of the solder wave. This blockage will result in poor solder connections on those thru-hole pins.
- Large thru-hole connectors with multiple pins must be placed so the parts travel perpendicular to the wave during wave soldering. The closer pins are in a line going through the wave, the more likely the trailing pins will not be soldered.
- Smaller individual discrete surface mount components should also travel through the wave perpendicularly so that both pins are soldered simultaneously. Correct placement of these parts requires the designer to know which direction the board will travel through the wave before the layout begins.
- When placing surface mount components to be wave soldered, avoid placing smaller components behind larger ones in the direction of the wave. Neglecting this could result in the larger parts shadowing the smaller ones and creating a poor solder joint.
- Multi-pin SMT parts such as ICs can be wave-soldered, but they should be placed in line with the direction of the wave to avoid shadowing the trailing pins.
- Be careful not to create land pattern pad shapes too large, as this could cause solder bridging between them. It is always best to follow IPC specifications when creating your PCB footprints.
- Remember that the wave’s height has limits, so taller components may prohibit that side of the board from going through the wave.
With the component placement optimized for wave soldering, your board can be assembled faster and with fewer problems requiring clean-up soldering by hand. An optimized placement will result in higher production yields, lower costs, and longer-term reliability for the board. The next step is to partner with someone who can help you with this placement optimization.
A wave soldering machine ready to solder a run of circuit boards
How Your Contract Manufacturer Can Help You Layout Your PCB for the Wave
Wave soldering is typically faster in both setup and soldering, making it the “go-to” process whenever possible. Wave soldering also gives better consistency over hand soldering. Even SMT boards will often go through the wave to get a more robust installation of their connectors and other thru-hole parts. With all of these benefits, it is evident that wave soldering is here to stay. The key is to get the best results from it.
Here is where the help of your PCB contract manufacturer can significantly assist you. At VSE, we have worked with many customers just like you who need the highest yields and quality in their circuit board manufacturing. Our wave soldering processes are fine-tuned to give you the results that you need, and our technical teams are ready to help you with any questions.
